The overall objective of the proposed work is to obtain an understanding of the function of deoxyribose 5-P aldolase and its role in the regulation of nucleoside and nucleotide metabolism in mammalian cells. Purine nucleoside phosphorylase, phosphopentomutase and other enzymes of nucleoside catabolism also will be studied in mammalian cell cultures to begin to understand the genetic regulation of these enzymes in eucaryotic cells and their role in cell growth and metabolism. The enzymes will be purified from rat liver and antibodies made to be used as a probe at the molecular level. Mutants of mammalian cells deficient in each of the above enzymes will be isolated, characterized and used to establish the metabolic function of the enzymes.